Political Correspondent

Leading immigration lawyer Julian Burnside has described the legal bid by Papua New Guinea opposition leader Belden Namah to close processing facilities on Manus Island as ''pretty realistic''.

On Wednesday, Mr Namah told the ABC he had engaged lawyers to prepare a Supreme Court challenge to the processing centre on constitutional grounds. The PNG constitution says people can be detained on the island only if they have been charged with a criminal offence.

Mr Burnside said the constitution also guaranteed the right to liberty and freedom of movement, which could be used in a legal challenge to the legality of the centre.

However, it appears Mr Namah's move will be strongly fought by the PNG government. In November, PNG Prime Minister Peter O'Neill said the new government was strongly committed to a permanent processing facility on Manus Island.

"I believe … [the] centre is necessary in Manus because it is becoming more relevant when we have huge illegal migration taking place - not only in Papua New Guinea but the rest of the Pacific Island countries,'' Mr O'Neill said.

''. . . this decision was made by the previous government and we, as a new government, are obligated to honour that''.